Electron multiplier tube



April 30,1957 D. A. JENNY ELECTRON MULTIPLIEIR TUBE 2 Sheets-Sheet 1Filed March 30, 1953 April 1957 D. JENNY 2,790,922

ELECTRON MULTIPLIER TUBE Filed March 39, 1953 2 Sheets-Sheet 2 INVENTOR.

2,790,922 Patented Apr. 30, 1957 United States Patent Oifice ELECTRONMULTIPLIER TUBE Dietrich A. Jenny, Princeton, N. J., assignor to RadioCorporation of America, a corporation of Delaware Application March 30,1953, Serial No. 345,301

10 Claims. (Cl. 313-105) The present invention relates to an improvedelectron multiplier device or tube, particularly suitable for use as apower tube for translating, amplifying, generating and/ or controllingradio frequency power at frequencies above tube especially adapted foruse at high frequencies.

The invention provides an electron multiplier tube comprising an arrayof electron multiplier or dynode elements 7 providing a plurality'ofdiscrete channels and a plurality of input cathode-grid structures orunits mounted adjacent the entrances to the channels to direct a streamof primary electrons into each channel. An embodiment will be describedand illustrated, by way of example, in which the primary streams for twoadjacent multiplier channels are supplied by a single cathode-grid.unit. However, it will be understood that a separate cathode-grid unitmay be provided for each channel if desired.

The invention will be illustrated with the type of multiplier structuredisclosed and claimed in a copending application of Russell R. Law,Serial No. 43,851, filed August 12, 1948, now Patent No. 2,674,661,dated April 6, 1954, assigned to the same Iassignee as the presentapplication, but it will be understood that the improved input structurecan be used with other types of multiplier structures without departingfrom the spirit 'of the present invention.

In the drawing:

Fig. l is a longitudinal sectional view of an electron multiplier tubeembodying the invention;

Fig. 2 is an enlarged detail sectional view showing two of thecathode-grid units and the adjacent dynode elements defining theentrances of four of the multiplier channels;

Figs. 3 and 4 are plan and sectional views of a dynode supporting disc;

Fig. 5 is a plan view of a spacer disc used in the dynode assembly; and

Fig. 6 is a detail view showing a portion of the cathodegri-d structureand its supporting means.

Referring to Fig. 1, the tube includes a pair of heavy copper rings 1and 3 between which are clamped, by bolts 5, a stack of metaldynode-supporthig discs 7 separated by insulating mica discs 9 and metalspacer discs 11. As shown in Figs. 3 and 4, each disc 7 has arectangular aperture 13 across which are mounted a row of metal dynodeelements 15 in spaced, parallel relation. The spacer discs 11 haverectangular apertures 17 which are larger than the apertures 13. Eachdisc 7 is sandwiched between two spacer discs 11, and each such group ofthree discs is insulated from the next group by a mica disc 9. The micadiscs 9 have rectangular apertures smaller than the apertures 13 in thespacer discs 11 to provide long leakage paths between the metal discs.The dynode elements of adjacent rows are staggered, as shown in Fig. 1and in the enlarged view of Fig. 2, with the elements of alternate rowsin alignment, to provide a plurality of parallel, discrete, electronmultiplier channels 21 each having as many secondary emission stages asthere are transverse rows of elements. Each of the dynode elements 15 isroughly rectangular in cross section with inwardly curving secondaryemitting surfaces to provide a suitable electric field for directing thesecondary electrons from element to element in each channel. In the tubeshown, the output of the tube is taken from two collector electrodes 23mounted adjacent the [outer side of the last row of dynode elements 15,preferably with transverse grooves 27 in which portions of the lastdynode elements are located. The collector electrodes are mounted onmetal lead-in and supporting rods 29 sealed through an insulating disc31. A pair of metal rings 33 and 35 are sealed between the heavy ring 3and the disc 31 to form part of the tube envelope.

The structure described so far is substantially identical with thatshown in Fig. 1.0 of said copending Law application. In said applicationthe input structure included a single cathode and means for deflectingthe beam of primary electrons therefrom between one half and the otherhalf of the multiplier structure, tov produce pushpull output from thetwo collector electrodes. This type of input structure involvesappreciable transit time efiects, particularly at very high frequencies,due to the unequal distances between the center of deflection and thedilferent portions @of the electron multiplier, and also due to thediffering path lengths of electrons over the beam crosssection betweenthe focal points of the beam, which limit the effectiveness ,of thetube.

In accordance with the present invention, an input structure, comprisinga separate cathode or emitting surfiace and closely-spaced control grid,is mounted near the entrance of each multiplier channel, or pair ofadjacent channels.

In Fig. 1, there are eight multiplier channels in each half of themultiplier section, fed by four input cathodegrid structures for eachhalf. As shown best in Fig. 6, each input structure comprises a cathodesleeve 37 indirectly heated by an internal heater wire or coil 39 and awire wound control grid 41. The cathodes and grids exten-d along thedynode elements 15 and are mounted in front of the dynode elements ofthe second row and be tween those of the first row. In transversesection, the grid 41 comprises a central circular portion 43, concentricwith the cathode sleeve 37 and closely and uniformly spaced therefrom,and two outwardly-extending end portions or loops 45 through which apair of grid support rods or wires 4-7 extend. A reflector electrode 49in the form of a flat metal plate is mounted close bebind thecathode-grid structures to direct the primary electrons from eachcathode 37 toward the first dynode element 15 of each channel. Ifdesired, due to the provision of the reflector electrode 49, the entiresurface of the cathode sleeve 37 may be coated with conventionalelectron emitting oxides. However, it is preferable to coat only thosesurfaces 50 of the cathode sleeve 37 which fiac'e toward the multiplierchannels, to conserve input power by eliminating unnecessary gridcurrent.

The eight cathode-grid structures are supported at their ends by twomica plates 51 which are attached to outwardly extending flanges on thereflector plate 49. The plate 49, as shown in Fig. 6, is mounted bymeans of end flanges 55 attached to lateral flanges 57 extending alongthe short sides of a rectangular aperture in a metal disc 59 which issimilar to the dynode element supporting discs 7 and is also clampedbetween the heavy rings 1 and 3. A mica disc 61 insulates the disc 59from the ring 1.

The envelope of the tube is completed by a cupshaped metal member 63soldered or welded to the heavy ring 1 and having a central aperture 65in which is sealed a glass plate 67. At least six leads 69 are sealedthrough the glass plate, 67 for connection to the cathodes 37, heaters39, grids 41, and reflector electrode 49. All of the cathodes 37 areconnected together and to a single lead 69. The grids 41 are connectedtogether in two groups with separate leads, one for each half of themultiplier section, to permit push-pull operation of the tube. However,it will be understood that the tube may be used as a simple amplifierwith all of the grids connected together, internally or externally, forhigh power operation with the sixteen multiplier channels in parallel.Direct current leads for applying successively increasing positivepotentials to the difierent rows of dynode elements 15 may be led outthrough the glass plate 67, or in any other conventional manner.

-As an example, in operation the tube electrodes may be provided withdirect current bias potentials as follows: cathodes -1500 v.; grids, -1to 10 volts negative with respect to the cathodes; reflector, about-l800 volts,

adjustable to produce maximum input efiiciency; first dynodes, -1200volts; last dynodes, zero volts (ground); collectors, several hundred toseveral thousand volts positive; and intermediate dynodes, suitablenegative potentials between -12OO and zero volts, depending upon thenumber of rows or stages of secondary emission used.

The input system of the invention reduces the transit time effects, inthe tube as compared to a single cathodedefiection input system, or asingle cathode-single grid input structure for all of the multiplierchannels, by providing short and uniform electron paths between thecathodes and associated grids and also between the grids and the firstdynodes.

What I claim is:

1. An electron tube comprising an anode, means including a plurality ofelectron-emitting cathodes spaced from said anode for producing a likenumber of primary electron streams, a control grid disposed closelyadjacent to each cathode for modulating each stream, and at least oneseparate electron multiplier section disposed in the path of each streamin the space between said grids and said anode.

each positioned closely adjacent to one of said cathodes,

an electron multiplier adjacent to said grids and including a pluralityof dynode elements providing a plurality of discrete electron multiplierchannels, at least one channel for each cathode, and an anode inposition to receive secondary electrons from all of said multiplierchannels.

3. A tube as in claim 2, wherein each multiplier channel includes atleast three dynode elements.

4. A tube as in claim 2, wherein each of said cathodes is located nearthe entrances to two adjacent multiplier channels in position to supplyprimary electrons to both channels.

5. A tube as in claim 2, further including reflector electrode meanslocated on the opposite side of each cathode from said electronmultiplier.

6. A tube as in claim 2, wherein said cathodes and dynode elements arearranged in parallel rows with adacent rows staggered to provide zig-zagelectron paths through said channels to said anode.

7. A tube as in claim 6, wherein each of said dynode elements comprisesa pair of oppositely-facing concave surfaces forming secondary electronemitting surfaces of two adjacent electron multiplier channels.

8. A tube as in claim 6, further including a reflector electrodeparallel to said row of cathodes and located on the opposite side ofsaid cathode from said dynode elements.

9. A tube as in claim 2, wherein each cathode comprises an elongatedcylindrical sleeve containing a heater element and each control gridcomprising an elongated References Cited in the file of this patentUNITED STATES PATENTS 2,433,700 Larson Dec. 30, 1947 2,492,976 FergusonJan. 3, 1950 2,591,012 Salisbury Apr. 1, 1952 2,636,141 Parker Apr. 21,1953 2,645,734 Rajchman July 14, 1953 2,674,661 Law Apr. 6, 1954

